Cycling and music. These are two things I'm passionate about. Why not combine them?

On a scale of 1 to 3, this project ranks a 2 in difficulty. You'll need to be able to solder, desolder, identify a few components and adapt this design to suit your application.

Total Cost
My out of pocket costs were $6. The plastic, speaker, zip ties, misc. wire were either found or leftovers from other projects.

Time
~1 hour once you have all supplies

Quality
From an appearance stand point - I give it a 9 out of 10
From a functionality stand point - I give it an 8 out of 10
From an audio stand point - I give it a 6 out of 10
From a loudness stand point - I give it a 7 out of 10
(A prior version of this would have had scores under 5)

As a side note - yes, this is technically not a stereo. Complaining about that is your prerogative, but I couldn't care less. If I say sharpie, you know it's a permanent marker - communication has been served.

Step 1: Materials

1 Amplifier
1 Speaker
1 Power Supply
Misc. Wire
Headphone jack
Mounting Board

Specifically

*$5 Harbor Fright Megaphone
*Free speaker from discarded boombox
*Batteries, AA's are fine - they need to put out ~6V (I later used a 6V gel cell) - you can also use the original battery pack if that suits you
*Wire, some wire came from boombox - I also used a Cat5 cable
*Headphone jack can come from a pair of headphones

For the mount, I used a piece of plastic that I then laser cut to fit perfectly into my bike rack - feel free to improvise, similar quality can be had using thin plywood and a jigsaw ;)

Step 2: Disassemble and Modify Megaphone

After a few minutes of playing with the megaphone, it's time to disassemble. You'll want to pay attention to where the power connections are soldered in the event they break off.

You'll need to desolder the microphone and then solder on a bit of wire - the length of which is based on how far your music player will be from your speaker.

Solder the headphone jack to the opposite end of the speaker.

At this point, you should be able to play music through the megaphone's original speaker.

Step 3: Remove Old Driver - Replace With New Speaker

Remove the old megaphone driver - while it's suitable for projecting sound a log distance, it's not very nice for anything more than scratchy vocals yelling at misbehaving schoolchildren.

Replace with another speaker - I sourced mine from a derelict boom box.

Check that you can still play music - this is also a good time to mock up mounting locations.

Step 4: Cut Mounting Board

I decided the best place to mount would be under my seat in my underseat rack. I cut a piece of plastic to fit that space with minimal gap - I also cut mounting holes, the speaker hole, spacers and screw holes for the speaker.

And, while I was at it, I laser etched and painted my crest for a little extra personalization. By raster cutting at l medium power levels while keeping the protective paper on, you can create clean looking paint by laser graphics. By etching, then painting, then etching the paint off, you can easily create multi-colored and multi level graphics with laser precision.

Step 5: Mount Hardware

The first version of this project used 4 D sized alkaline cells - these lasted a long long time.... Ultimately, I ended up using a small 6V sealed lead acid battery for rechargeable goodness.

The second picture shows the plastic spacers used to interface with the boom box speaker's mount. Also notice the zip tie holding the blue cat5 cable to the circuit board to serve as strain relief in the event the cord should ever get tugged on. This turns out to be absolutely necessary.

The circuit board is mounted to the speaker on one of the machine screws.

Step 6: Mount to Bike

Now, it's time to mount to your bike. If you thought ahead, this should be fairly straightforward.

I'm using zip ties because
a) Plastic
b) Don't Corrode
c) Cheap
d) Are available in the reusable variety
e) Lots of colors

Step 7: Have a Party!

Now go cruising! Safely and in style!

Later, at an intern beach party - the bike mono-o turned into our awesome mobile music delivery system.

1st Picture: Ocean Beach, CA
2nd Picture: Aaron makes and plays the kelp-o-phone!